Refactor some internals of wasmtime-cranelift (#4202)

* Split `wasm_to_host_trampoline` into pieces

In the upcoming component model supoprt for imports my plan is to reuse
some of these pieces but not the entirety of the current
`wasm_to_host_trampoline`. In an effort to make that diff smaller this
commit splits up the function preemptively into pieces to get reused
later.

* Delete unused `for_each_libcall` macros

Came across this when working in the object support for cranelift.

* Refactor some object creation details

This commit refactors some of the internals around creating an object
file in the wasmtime-cranelift integration. The old `ObjectBuilder` is
now named `ModuleTextBuilder` and is only used to create the text
section rather than other sections too. This helps maintain the
invariant that the unwind information section is placed directly after
the text section without having an odd API for doing this.

Additionally the unwind information creation is moved externally from
the `ModuleTextBuilder` to a standalone structure. This separate
structure is currently in use in the component model work I'm doing
although I may change that to using the `ModuleTextBuilder` instead. In
any case it seemed nice to encapsulate all of the unwinding information
into one standalone structure.

Finally, the insertion of native debug information has been refactored
to happen in a new `append_dwarf` method to keep all the dwarf-related
stuff together in one place as much as possible.

* Fix a doctest

* Fix a typo

crates/environ/src/lib.rs

@@ -70,28 +70,3 @@ pub const WASM64_MAX_PAGES: u64 = 1 << 48;
 
 /// Version number of this crate.
 pub const VERSION: &str = env!("CARGO_PKG_VERSION");
-
-/// Iterates through all `LibCall` members and all runtime exported functions.
-#[macro_export]
-macro_rules! for_each_libcall {
-    ($op:ident) => {
-        $op![
-            (UdivI64, wasmtime_i64_udiv),
-            (UdivI64, wasmtime_i64_udiv),
-            (SdivI64, wasmtime_i64_sdiv),
-            (UremI64, wasmtime_i64_urem),
-            (SremI64, wasmtime_i64_srem),
-            (IshlI64, wasmtime_i64_ishl),
-            (UshrI64, wasmtime_i64_ushr),
-            (SshrI64, wasmtime_i64_sshr),
-            (CeilF32, wasmtime_f32_ceil),
-            (FloorF32, wasmtime_f32_floor),
-            (TruncF32, wasmtime_f32_trunc),
-            (NearestF32, wasmtime_f32_nearest),
-            (CeilF64, wasmtime_f64_ceil),
-            (FloorF64, wasmtime_f64_floor),
-            (TruncF64, wasmtime_f64_trunc),
-            (NearestF64, wasmtime_f64_nearest)
-        ];
-    };
-}